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refs: fix segfault when aborting empty transaction

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When cleaning up a transaction that has no updates queued, then the
transaction's backend data will not have been allocated. We correctly
handle this for the packed backend, where the cleanup function checks
whether the backend data has been allocated at all -- if not, then there
is nothing to clean up. For the files backend we do not check this and
as a result will hit a segfault due to dereferencing a `NULL` pointer
when cleaning up such a transaction.

Fix the issue by checking whether `backend_data` is set in the files
backend, too.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt 2020-03-30 15:46:13 +02:00 committed by Junio C Hamano
parent 3bab5d5625
commit edc30691e5
1 changed files with 11 additions and 9 deletions
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20
refs/files-backend.c
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@ -2565,17 +2565,19 @@ static void files_transaction_cleanup(struct files_ref_store *refs,
}
}
if (backend_data->packed_transaction &&
ref_transaction_abort(backend_data->packed_transaction, &err)) {
error("error aborting transaction: %s", err.buf);
strbuf_release(&err);
if (backend_data) {
if (backend_data->packed_transaction &&
ref_transaction_abort(backend_data->packed_transaction, &err)) {
error("error aborting transaction: %s", err.buf);
strbuf_release(&err);
}
if (backend_data->packed_refs_locked)
packed_refs_unlock(refs->packed_ref_store);
free(backend_data);
}
if (backend_data->packed_refs_locked)
packed_refs_unlock(refs->packed_ref_store);
free(backend_data);
transaction->state = REF_TRANSACTION_CLOSED;
}